When a geostationary satellite is launched, the hope is that the satellite will land in a circular orbit above the equator at an altitude of 35,800 kms. When properly located in this orbit, the satellite will move in a circular orbit in time with the rotation of the earth about its polar axis so that the satellite appears from any point on earth to be stationary. The geostationary satellite also has a 0.degree. inclination relative to a plane drawn through the equator. In order to maintain the satellite in this position, thrust engines must be periodically fired on the satellite, usually under the control of a ground station. The fuel and thrust engines necessary for this purpose usually account for approximately 40% of the initial weight of the satellite that is launched into space.
When a geostationary satellite is launched and something unanticipated occurs, it is possible for the satellite to land in space close to, but not at, the desired geostationary position. The thrust engines on the satellite can then be used to maneuver the satellite into its proper parking position in the equatorial orbit. The amount of fuel used in maneuvering the satellite can be significant and has a direct effect on the useful lifetime of the satellite. A typical geostationary satellite uses up its maneuvering fuel over the course of approximately 7 to 8 years. The electronics on board the satellite can still be functioning properly; however, the fuel is no longer available to maintain the satellite in its parking place above the equator. The consumption of this fuel in maneuvering shortens the useful life of the satellite.
In a recent launch of a geostationary satellite, an anomaly occurred during the launch which caused the satellite to not land in its proper geostationary position. The decision was made to not consume the fuel needed to move the satellite into its proper spot; rather, the satellite was let free to orbit at an inclination of approximately 1.8.degree. relative to the equatorial plane. A satellite orbiting the earth in an inclined axis tends to assume a figure 8 configuration with the crossover point of the 8 being located over the equator. The satellite then moves in an elongated figure 8 configuration ascending upward toward the northern hemisphere to a maximum excursion point and then descending to cross the figure 8 to a southern maximum excursion point and then back north again.
The usual method of following a satellite in space, particularly a satellite in a high inclination elliptical orbit, is to focus an antenna on the satellite and then, use an appropriate servo system, and RF peak sensing to maintain the antenna focused at the satellite. The antenna mount must be a complex mechanical structure in order to allow the antenna to move in azimuth plane and in elevation to follow the satellite. The same technique can be used to follow a geosynchronous satellite moving in an inclined orbit. In either case, the electronics and hardware required for tracking the satellite are extremely complex and expensive.